In order to explore the possibility of improving the quality of periclase in the melting process, we studied the impurity distribution in the body of the block. For conducting chemical analysis and electrophysical investigations, periclase samples were selected along certain vertical and horizontal axes lying in the cross section of the block during the stripping (finishing) process.It was established that the migration of impurities from the bottom zone of the electrode takes place more effectively towards the peripheral region of the block (1.8-3 times) than towards its central region. The transfer of impurities towards the peripheral layers of the block is more effective (1.5-2.7 times) in the radial direction than in the vertical direction.Based on the established nature of impurity distribution across the cross section of the block, it may be considered that the inverse liquation (negative segregation) occurring along the horizontal lines of the block forms the main driving force for the impurity migration towards the periphery of the block, i.e., towards the low-temperature zone.The phenomenon of capillary-pressure development within the two-phase region of a solidifying melt forms the basis for the inverse liquation process; this capillary pressure originates because of the difference in the values of the interracial tension at the boundary of the melt having the average composition and the contaminated melt (enriched with impurities) with the solid phase [i]. Therefore, the liquid magnesium oxide enriched With impurities is forced out of the capillaries of the two-phase region towards the peripheral portion of the block.These facts make it possible to conclude that it is advisable to develop inverse liquation during the forming process of the periclase block. To this end, it is essential to reduce the cooling rate of the melt in the liquid-solid state, it was previously shown [i, 2] that a reduction in the cooling rate of the melt facilitates widening of the two-phase region where the liquid and the solid phases coexist, and that the capillary-porous structure of this state helps in creating the capillary pressure and developing zone liquation.It is possible to decrease the cooling rate, and thereby to decrease the crystallization rate, by following an interrupted melting practice that consists of alternate periods of intense melting of magnesite and of holding the melt at the melting temperature, i.e., with periodic Variation in the power input to the furnace [3].The cooling of the melt was slowed down by alternation of the working periods of the furnace on the first and the ninth voltage steps of the transformer, and by additional variation of the arc current.Alternation of the minimum and the maximum power of the arc created the conditions for zone refining, i.e., for repeated decontamination of the remelted upper layers of periclase.During this process, the depth of the melt was retained at 350-400 mm, which is typical for the furnace operation on the first voltage step of the transformer. The bath ...
The production of periclase is characterized by a substantial yield in the arc process of returnable underfused material (partly melted ) [i]. The repeated use leads to the accumulation in it of impurities and the formation of reject undermelted material (Fe203 > 0.35%, CaO > 3%); it also impairs the quality of the periclase and increases the consumption of raw materials per unit product.The rational use of raw materials and an increase in the product quality can be obtained by beneficiating the underfused material.The high concentration in the material of impurities including iron oxides and the action of reducing atmospheres, the formation of which is connected with combustion of the electrodes, causes the presence in the undermelted material of metallic inclusions possessing strong and weak magnetic properties.The grinding of the undermelted material contributes to the opening-up and release of the magnetic particles, and makes it possible to extract them in a magnetic field.According to microscopic and x-ray structural investigations, the main impurity phases in the material consist of monticellite, ferromonticellite, and forsterite.The volume proportion amounts to from 2.4 to 6.6%.Some samples contained free calcium oxide. The content of inclusions of aluminum and iron spinels, magnesioferrite and magnetite equals from 0.3 to 1.5%. The metallic inclusions in amounts of 0.2-0.5% are contained in the finest and coarsest fractions.* The magnetic susceptibility of the separated minerals in the series magnetite-magnesioferrite-spinels varies in wide limits, from 1.28 x i0 "2 to 60 • 10 -8 m~/kg.The extraction from the underfused material of strong ferromagnetic materials is carried out in a magnetic field with a force of 100-130 kA/m.The weakly magnetic inclusions in the material are extracted in a field of high strength [2]. The completeness of the extraction of the magnetic and related components depends on the strength of the field in the separator and the size of particles of the underfused materials.We studied several samples of material distinguished by their concentration of impurities.In order to separate the magnetic particles we used a magnetic separator of the type 138T.Before the separation of the weakly magnetic fractions it is necessary to purify them to remove the strongly magnetic particles.The milling size, starting from the need to open the grains and ensure effective milling of the magnetic impurities, does not exceed 3 mm. The thickness of the layer of underfused material on the separator tray is not greater than the dimension of the fraction being beneficiated, that is, from 0.5 to 3 mm. The distance from the layer of underfused material to the roller was regulated respectively within the range 1-7 mm. Charging of the undermelt in the magnetic zone of the seperator was up to 3 kg/h. In order to explain the relationship between the extraction of the magnetic fraction and the strength of the field we used the return and reject undermelt fraction less 2 mm. After extraction of the strongly magne...
The mechanism of formation of harmful components of anode gases of aluminum production is considered. For purification of anode gases the nepheline slime, which is alumina withdrawal from nepheline ore, is offered as adsorbent and the catalyst. The new design of a gas-collecting bell of the Soderbergh,s electrolyzer for collecting and thermal neutralization of anode gases with adjustable air supply is developed.
I. Storozhev, V. V. Mechev, E. V. Smirnova, UDC 666.762.32.046.4.012.7 V. V. Skorodumov, and G. A. Chernov On the basis of material and thermal balances of magnesite heats in an electric arc furnace made at Northern Angar Periclase Plant* it was found necessary to transfer the endothermic process of decarbonization and low temperature burning to a separate preheater for purposes of increasing the production of periclase.
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